Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a first embodiment of a display screen or portion thereof with a graphical user interface;

FIG. 2 is a front view of a second embodiment thereof;

FIG. 3 is a front view of a third embodiment thereof; and,

FIG. 4 is a front view of the graphical user interface, seen without the display screen for ease of visibility.

The broken line showing of the display screen, portions of the display screen, text and graphical elements form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described herein. 